1. Field of the Invention
This invention is directed to an apparatus and to a method. More specifically, this invention relates to a three-conductor booster cable assembly and to a method for real-time control of the power transfer through the booster cable assembly from a power source to a battery which is being charged from the power source.
2. Description of the Prior Art
The potential hazards in the use of booster cables for charging of lead-acid batteries, the type commonly found in automobiles, boats and other vehicles, is fully appreciated by the prior art. Batteries of this type internally generate hydrogen and oxygen gases (at the plates of the battery) which are highly explosive. In the event these gases escape and collect in the vicinity of the terminals of the battery, they can be ignited by any sparks or arcing at the terminal. Care must, thus, be taken to maintain the areas around the battery free from sparks, etc. in order to prevent combustion of these gases. The effect of such combustion would be to rupture the batatery casing, causing the electrolyte (sulfuric acid and water) to be sprayed or spilled over any individual or object in the immediate vicinity, with potentially serious injuries resulting.
The jumper cables which are commonly used for jumpering batteries consist of two (2) conductors. These cables are typically accompanied by specified hook-up instructions from the manufacturer in order to reduce the danger of arcing at the battery terminals. Notwithstanding the precautions taken by both the manufacturer of such cables and by the user, the potential for ignition of the explosive gases in the vicinity of the battery terminals is everpresent.
Modification to conventional two-conductor cable design has been attempted to reduce this potential hazard. The evolution of cable design over the years has been both imaginative and varied. These designs generally involve the provision of some physical or electronic device to prevent or interrupt the flow of current along such cables where the potential for arcing was detected. These electronic devices can themselves be further grouped into two subcategories: (a) electronic devices incorporating safety circuitry along at least one of the conductors of the battery cables to prevent the flow of current through the cables, unless the cables are properly connected, and (b) electronic and/or electromechanical devices incorporating what has been termed "terminal blocks", which permit reversal of incorrectly connected cables to the appropriate polarity conditions.
The following patents are representative of the prior art approaches to providing a resolution to this problem: U.S. Pat. Nos. 3,654,538; 3,659,183; 3,809,993; 4,163,134; 4,166,241; 4,233,552; 4,349,774; 4,463,402; and 4,607,209.
To aid in the understanding of the significance of the contribution of the instant invention, two figures (FIGS. 2 and 3) have been included in this disclosure to illustrate the most relevant prior art. All of the relevant prior art, including the cable assemblies illustrated in FIGS. 2 and 3 are based upon a booster cable consisting of two (2) conductors; one conductor for connection of the positive terminal of the power supply to the positive terminal of the battery, and a second conductor for connection of the negative terminal of the power supply to the negative terminal of the battery. FIG. 2 is a block diagram of the safety circuit of U.S. Pat. No. 4,607,209. In brief, this safety circuit diagram illustrates a normally open relay (208) which has been placed intermediate between two terminal clamps (210, 212) along a common conductor (232, 242). Unless certain conditions are fulfilled, the terminal clamp 210 of cable 232 will remain electrically isolated from terminal clamp 212 which is connected to cable 242, thus preventing current from flowing therebetween. The conditions are such that the clamps of the cables must be connected to the correct terminal polarities of both the power source and the battery to be recharged. The circuit which is illustrated can, of course, work in either direction, that is, cable pair 231/232 can be connected to the power source with cable 241/242 connected to the battery; alternatively, cable pair 231/232 connected to the battery and cable pair 241/242 connected to the power source. For the sake of simplicity, the circuit operation is described assuming that cable pair 232/231 is connected to the power source. The preferred embodiment of control circuitry which is described in the '209 patent contemplates a solenoid as the normally open relay.
Conductor 242 is connected to a polarity indicator (201) as is conductor 232. These polarity indicators (201, 202) alert the user when the cables have been connected to the correct terminal polarities. In the example illustrated in the block diagram, the conditions of the circuit would be satisfied if cable 232 were connected to the positive terminal of the power source and cable 231 were connected to the negative terminal of the power source, and cable 242 were connected to the positive terminal of the battery to be recharged and cable 241 were connected to the negative terminal of the battery to be recharged. The preferred polarity indicators suggested in patent '209 are light emitting diodes. If the cable connections are not properly made, one or both light emitting diodes would not be armed, thus alerting the user to a potential problem.
The logic circuit (206) of the block diagram operates the normally open relay (208). This circuit performs a logic AND function, that is, when the correct connections have been made to the power source and to the battery, the logic circuit will close the relay. Where any of the connections have not been made or have been made incorrectly, the logic circuit will be unable to effect closure of the relay.
While the circuitry of the '209 patent provides safety features not previously available in other prior art systems, additional modification was still needed to prevent arcing at the terminals in those situations in which the user had failed to effect solid physical contact between the cable clamps and the terminals of the battery, or of the power source, at the time of their initial connection.
This shortcoming was remedied by providing additional time delay circuitry (303, 304) which prevents the logic circuit (306) from activation of the normally open relay (308) until some finite period after the cable clamps have been securely affixed to the respective terminals of the battery and the power supply. FIG. 3 is illustrative of an improvement of the booster cable assembly of the '209 patent which addressed the arcing problem during the initial connection of the cable clamps to the terminals of this power supply and battery to be recharged. This improvement to the '209 patent is described in co-pending PCT application, U.S. 86/00876, filed Apr. 25, 1986.
While the imposition of a finite delay between the satisfaction of the requisite conditions for current flow, and the actual closing of the normally open relay, does enhance the safety of the battery cables, it still cannot prevent arcing from occurring, after initial connection of these clamps to the terminals, in the event that one of the cable clamps is inadvertently and unintentionally disconnected from either the positive terminals of the battery or of the power source after flow of current has commenced. Accordingly, further improvement is both desirable and essential in order to protect the user of booster cables against potential ignition of explosive gases in the vicinity of the battery, both at the time of installation of the battery cable and during the actual charging cycle.